Western Australia's south is currently shimmering with a golden flowering plant — but biologists say it's a very attractive pest.
Key points:
- The Sydney golden wattle is one of around a thousand species of acacia native to Australia
- It was introduced to WA from the eastern states and has become a pest
- Environmentalists say it is choking out indigenous wattle species and is hard to eradicate
The Sydney golden wattle — or Acacia longifolia — has reached plague proportions in Western Australia's south.
It is considered a pest by conservationists and thrives in the conditions of the south coast, where it is abundant in bushland this time of year, but can squeeze out other varieties of wattle that are native to the state.
Professor Stephen Hopper is a conservation biologist in the Great Southern and said the Sydney golden wattle was the most pernicious woody weed in his part of WA.
"It is very attractive. It's in full flower at the moment and can get up to 10 metres high as trees, so a real big splash of gold and yellow in late winter," he said.
But while beautiful to look at, it can spread like wildfire if left unchecked.
Seeds spread by birds, animals
The Sydney golden wattle was introduced to WA as a horticultural plant and is one of almost 1,000 species of wattle around the country.
Some are indigenous to the state, but the Sydney golden wattle has been introduced in the west.
"It's native to the east coast of Australia, Tasmania, right up into northern New South Wales and Queensland, [and] often near the coast, it seems to thrive," Professor Hopper said.
He said it tended to take over as it could establish itself in undisturbed bushland, reducing agricultural productivity and loss of native habitat.
"Sydney [golden] wattle has its seeds spread by animals, by birds mostly," Professor Hopper said.
"The seed just has to plonk into the ground and winter rains come along, and [they] germinate, and away they go."
War of the wattles
The wattle has remained a sentimental icon of Australia for more than 200 years, and usually signals spring is not too far away.
The golden wattle (Acacia pycnantha) — which has round flowers and looks quite different from the Sydney golden wattle — was officially proclaimed the Floral Emblem of Australia on September 1, 1988.
The Sydney golden wattle's flowers, however, are cylindrical like sausages, with two very prominent veins running lengthwise down their leaves, which are about five to 10 centimetres long.
According to the Department of Primary Industries and Regional Development's Western Australian Organism List, the Sydney golden wattle is not assigned to any local government area control category.
But South West horticulturalist Steve Wood agreed that, while very pretty, Acacia longifolia is a pest in the Great Southern region.
"They look so gorgeous and if they're in a home environment, they put on a beautiful show, they grow fast, they provide a screen, so it's just hard to be angry at them," he said.
However, they were greedy regarding their territory.
"Their seeds are so viable, whether they're being transferred by birds or whether it's by people pruning, they seem to establish," Mr Wood said.
"They take the space in the bush, and … ultimately, it's at the expense of our other beautiful local species."
One such species is the red-stemmed wattle, which Professor Hopper said needed protecting in the state's south.
"[It's] a much smaller shrub, called Acacia myrtifolia," he said.
"It has just a single vein on its leaves."
Unlike the Sydney golden wattle, the red-stemmed wattle has rounded flowers.
Bush turns golden
Professor Hopper said bushwalkers could easily spot the Sydney golden wattle growing of its own accord in the wild.
"I know places where it's not being managed at all," he said.
"What was a jarrah [and] Albany blackbutt forest has converted into an area of almost solely mono-specific Sydney [golden] wattle.
"It just produces tens of thousands of seeds, [and] hundreds of thousands in really big specimens."
Those seeds would last in the soil for at least 10 years, Professor Hopper said.
"You might get rid of the adult plant but you will have to go back and repeat the exercise pulling out seedlings for up to 10 years to make sure you've really got a hold on it," Professor Hopper said.
"If it's not managed, then it will just thicken up and smother everything else."
Greenskills Albany operations manager Jason Balhorn removed Sydney golden wattles on a large scale in the Great Southern and said it could be challenging.
"The introduction of heavy machinery does cause more problems," he said.
"Using them to drag stuff out, you tend to activate the ground that allows what we call woody weeds to take hold.
"We tend to thin out as much as we can, leave some in situ, and do what's known as a chemical ringbark."